Interface unit for a telephone exchange

ABSTRACT

An interface unit is provided for connection between each of a plurality of peripheral devices and a central processing unit. The peripheral devices include such things as subscribers lines, trunks and junctors. The interface unit includes a temporary memory for storing status information or instructions regarding the peripheral devices. A permanent memory delivers regulating signals for scanning current test inputs and comparing them with data stored in the temporary memory. When there is a discrepancy in the data in the memories, the unit calls the central processor and sends its information to the central processor, where it is processed and new data is sent back to the unit.

[56] References Cited UNITED STATES PATENTS 3,532,827 10/1970 Ewin l79/l8 ES X Primary Examiner-William C. Cooper Attorneys-C. Cornell Remsen, Jr., Walter J. Baum, Percy P.

Lantzy, Warren Whitesel, Delbert P. Warner and James B.

Raden ABSTRACT: An interface unit is provided for connection between each ofa plurality of peripheral devices and a central processing unit. The peripheral devices include such things as subscribers lines, trunks and junctors. The interface unit includes a temporary memory for storing status information or instructions regarding the peripheral devices. A permanent memory delivers regulating signals for scanning current test inputs and comparing them with data stored in the temporary memory. When there is a discrepancy in the data in the memories, the unit calls the central processor and sends its informa' tion to the central processor, where it is processed and new Jacques Henri De Jean Ris-Orangls, Essone; Marc Jean Pierre Leger, Issy-Les- Moulineaux, IIauts-de-Seine; Claude Paul Henri Lerouge, Maurepas, Yvelines, all of France App]. No. 835,541

June 23, 1969 [45] Patented Dec. 7, 1971 Assignee International Standard Electric Corporation New York, N.Y.

Priority June 28, 1968 France 157201 INTERFACE UNIT FOR A TELEPHONE EXCHANGE 11 Claims, 9 Drawing Figs.

United States Patent [72] Inventors [22] Filed Rpz .92 la fro/v can 7:

E a a m C LM 0 mm W 1 v we l w 2 (w J 0 0.7 w M01 0 Z n I I w m 1 J wm twfl K m t f I1 Ill a if M Q a '22 0 w b w x1 m w. W m w u a .m 4 mm l Wm m u M w mm d 2 m 0 JJIIJ QQ d AK Vm S43 |l| llllll ||l illl E E 300 N l W4W I: T ih T n r m mfu arm m mi s 1 mm :mm m M t i m G". -E- m r. flw I. Jr. W m n l m m m w W w E! ll I m m m N M m mh MM MM A "we m l llll mew umm w H M wwfi Attorney PATENTEDHEC Han SHEET 1 BF 4 INTERFACE UNIT FOR A TELEPHONE EXCHANGE The present invention concerns a circuit for controlling, in a data processing system, the connection between a plurality of peripheral equipments and a central processing unit which may be constituted either by a stored program computer, or by a wired program circuit.

In a particular case, taken by way of example, the system considered may be a telephone exchange wherein the peripheral equipments or peripheral units are the subscribers lines, the cross-points of the switching network, the junctors, the multiselector bars, etc.

A connection between a peripheral unit and the central processor is set up each time data must be transmitted, in either direction between these elements. This data is such that it is useful in the performance of various telephonic functions such as,,on the one hand, the line trunk, junctor or network supervision and; on the other hand, the control of the bars in a multiselector, digit reception, fault detection, etc.

The universal connection circuit according to the invention or connection unit which is designed for assuring the connection between a group of peripheral units and the central processor has been designed in order to enable its achievement into one single monolithic integrated circuit and it may assure any one of these functions without any modification of its internal wiring.

A connection unit provided for cooperating with x peripheral units comprises m input terminals (Xg m) connected partly or totally to said peripheral units in order to test their state, a memory with m flip-flops in which will be stored, for instance, the previous state of the tested units and m out put terminals connected partly or totally to the peripheral units in order to transmit therethrough the orders received from the control unit.

The supervision of the states of the peripheral units connected to the inputs and the transmission of this data to the processor unit are carried out cyclically under the control of m scanning signals delivered by a main clock.

In a mode of achievement of a telephone exchange, designed preferably for a small capacity exchange such as a private exchange (PABX), these connection units have access to the processor through random selection circuits connected in chain and which are able to select at random one unit among those which are calling for connecting it to the inputoutput circuit of the processor.

A connection unit appears to be calling when one has detected, by the cyclic scanning of the inputs, a change of state in one of the peripheral units. Besides, when the control unit wants to know the state of one peripheral unit or to transfer an order to it, the selection of the corresponding connection unit is carried by sending to the unit an order which sets it in the calling state in such a way as this call has automatically a high priority level.

It is thus seen that, in this organization, the data transfers between connection units and the processor do not require any priority circuit and are carried out without the intervention of an interrupt routine or of interrupt instructions.

The data processing in the central processor is carried out in a well-known way by means, either of a wired program or a number of stored secondary routines. Thus, when the connection is established between a connection unit and the processor, this latter receives the identification codes of the connection unit and the content of its memory. This information, which defines the type of function carried out by the unit (line supervision, digit reception etc.), its identity and-eventually-the state of advancement of the operation, enable to selectin the case of a stored program, the required routine. At the end of the processing, the results are transmitted to the connection unit so that the capacity of the fast memory as sociated to the processor is significantly reduced since said memory stores only the data related to the elementary operation which is being made.

Nevertheless, when the connection unit is associated to a digit receiver, the infonnation related to the advancement of the digit reception is well stored in the memory of said unit but it is realized that the register itself, which is the unit in which the digits are assembled, must occupy an address in a call memory associated to the processor.

On the other hand, the programming is very simplified since the supervision operations are programmed cyclically.

The object of the invention is thus to achieve, for a data processing system, a universal connection unit linking a number of peripheral units to a central processor which enables to carry out, in said peripheral units, state tests, commands the control of the state of advancement of operations, data storage etc.

Another object of the invention lies upon the face that all the connection units are identical whatever may be the executed function.

A feature of the invention is that a main clock delivers in a cyclic way, signals to, ill, 12.... tm, of equal duration; that each universal connection unit comprises first m inputs El, E2...Em selected cyclically by the signals :1, t2... rm, second a temporary memory comprising m flip-flops G1, G2... Gm the outputs of which are selected by the signals :1, 12... lm, third a permanent memory delivering a signal Cc at each of the pl scanning times (pl 5 m) which correspond to pl test inputssuch as the input E] ---which are connected to peripheral units in order to test their state, fourth a comparator which delivers, at time I], a disparity signal M when the state of the test input Ej is different from that of the flip-ilop Gj and fifth an inputoutput circuit comprising a call flip-flop B which is put to the 1 state either by a signal M or by the control processor of the telephone exchange when this latter wants to select the considered connection unit.

Another feature of the invention is that the connection between one calling connection unit: (N1, N2...Nk ...Ny) and the input-output circuit ll) of the processor is carried out through selection circuits grouping n connection units, and said selection circuits being connected so that there is a multilevel selection, that each of said selection circuits comprises a multistable circuit with n+1 stable states and a transfer circuit assuring a bidirectional transfer of data between the selected connection unit NI: and the circuit 10, that the first selection level comprises 2 selection circuits, that the multistable circuit of each selection circuit is connected to the I outputs of the call flip-flops ofn connection units, that said circuit delivers, when the call flip-flop Bk of the unit Nk is in the I state, an activation signal of the transfer gates associated with said unit and a call signal of the next selection level etc... and that, if several connection units are simultaneously calling, said multistable circuit chooses one of them without any ambiguity and at random.

Another feature of the present invention is that, when the processor wants to select directly the unit Nk, it transmits simultaneously, at the initial time, a signal 2 to all the connection units of the central exchange which resets all the call flipflops and a signal Dk which sets to the I state the flip-flop Bk so that only the unit Nk is calling and that it is immediately connected to the circuit It], the signal Dk being delivered by the decoding of the identification code of the unit Nk.

Another feature of the present invention is that, when the unit Nk is selected by the call either of a peripheral unit or by the control unit, the states of the inputs El, E2... Em and of the flip-flops G1, G2... Gm are transferred, through the various selection stages, to the circuit It) as well as the identification codes of the connection units and of the used selection circuits that, when the call originates from a peripheral unit, the comparison of these signals in the said circuit l0 gives the identification code of the first input whose state has changed and that this information is processed under the control of the processor program.

Another feature of the present invention is that, when the data processing is completed in the processor, a signal Dk is transmitted to the unit Nk so as to block the operation of said unit and that the information supplied by the processor is transferred to said connection unit under the control of the signals 11, t2... tm.

Another feature of the invention is that the universal connection unit may perform without any modification of its internal wiring, any test, data collection, operation command and operation control of functions, that the state test function of peripheral units is carried out through the a..t=pl inputs connected to suitable points of x peripheral units (a being an integer number such as 2 represents the number of possible different states), the a.x homologous flip-flops of the temporary memory being associated respectively to these peripheral units in order to store therein, under the control of the processor, the previous state informations, that the function of collecting the data elaborated in the peripheral units is carried out through b.x.=p3 inputs (b being the number of digits to be collected), that one has pl+p3 sm, that the operation command function, in the peripheral unit I-lj, is obtained by transmitting an order to the jth group of order flip-flops reserved to this function with c.x=p 4, that the operation control function, in the peripheral unit Hj, is obtained by transmitting an operation code to the jlh group of d operation flip-flops reserved to this function with d.x=p2, that the order and operation flip-flops may be homologous to the data collection inputs and that one has pl-l-p2+p4 g m.

Another feature of the invention is that the series of signals Cd, supplied by the permanent memory during one cycle of the scanning signals :1, 12... tm, may be used as a function code characterizing the type of function fulfilled by the connection unit, and that the functions for which pl=m may be differentiated the ones from the others in leaving free one input of different index according to the function.

The above-mentioned and other features and objects of this invention will become apparent by reference to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 represents the general diagram of the organization of a telephone exchange equipped with connection units;

FIG. 2 represents the general diagram of the clock;

FIG. 3 represents the detailed diagram of one universal linking unit;

FIG. 4a to 4c represent diagrams of signals supplied by the clock;

FIG. 5 represents the general diagram of a selection circuit;

FIG. 6 represents the topology of an assembly of connection units and of an associated selection unit designed in largescale integrated circuits;

FIG. 7 represents the detailed diagram of an input-output circuit associated to the central processor.

In order to facilitate its reading, the description will be divided as follows:

I. General diagram l.lDescription (FIG. 1) l.2-Clock (FIGS. 2 and 4) 2. Linking unit 2. 1 Description (FIG. 3) 2.2--Operation 2.2lCall 2.22Transfers of information to the selected connection unit 2.23-Disconnection 3. Utilization of the connection units 3. l-Assignment of the inputs and the flip-flops 3.2Specialization of the connection units 3.3-Digit supervision 4. Selection circuit (FIG. 5)

5. Topology (FIG. 6)

6. Input-output circuit I0 (FIG. 7)

6. l lntroduction 6.2-Description and operation 7. Identification I. GENERAL DIAGRAM l. 1 --Description FIG. I represents the general diagram of the organization of a central exchange comprising the universal connection units N1, N2.... Ny.

Each connection unit, such as the unit NI, comprises m inputs E1, E2... Em and m outputs A1, A2... Am, these 2m terminals being intended for being connected to suitable points of at mostm peripheral units. The inputs of one connection unit are used, for instance, to test the state of the peripheral units to which it is associated (line, junctor, state test, etc.) this test being carried out cyclically under the control of clock signals ll, :2... rm assigned respectively to the test of the inputs El, E2... Em.

One has shown also on FIG. I:

The input-output circuit l0 of the central processor CP,

The random selection circuits which control the connection between the connection units and the circuit l0. These circuits are cascaded in such a way as to constitute several selection levels. Thus the first level or level I comprises circuits RPl, RP2... RPz, each of these circuits being connected by means of n conductors to n connection units and having, moreover, three conductors or groups of output conductors connected to the circuits of the level II. This level II comprises the group of circuits RPo and has z inputs and three conductors or output groups of conductors.

By way of example, one will choose z=n and y=m so that the selection comprises two levels and the selection units are identical.

Besides the inputs and outputs E1 to Em, Al to Am, the connection unit N1 has first an output B1 on which a signal appears when the unit is calling (for instance when the state of one of the peripheral units to which it is connected has just changed) and second an output C1 grouping four conductors Ca, Cb, Cc, Cd on which are carried out the transfers of information between the unit and the circuit l0.

A selection circuit such as the circuit RP] of the level I comprises:

1. The multistable circuit MSl which has m+l stable states referenced 0 state, I state... m state. The states 1, 2... m are characterized by the occurrence of a state signal, respectively, on the outputs F 1, m and the 0 state by the logic condition FO=F1.F2... Fm, the sign showing symbolically the logical AND function. The switching of the circuit MSl to a state other than the 0 state, the state k for instance, is carried out when the connection unit Nk is calling. It will be seen further on (paragraph 4) that the circuit M51 is so designed that, if for instance it receives simultaneously signals B1 and B2, it sets itself without any ambiguity in either of the l or 2 states this constituting random selection. Besides, the circuit MSl supplies, for the condition F o, on the one hand a code identifying the calling connection unit which appears on the output K, and on the other hand, a call signal J1 for the level selection circuit II.

The multistable circuits of the circuits RPZ, RP3... RPz and RPo are identical; the state outputs of the circuit RPO being designated by UL m and its code output by K 2. The transfer circuit TGl which connects, under the control of the state signal Fk, the groups of conductors Ck and K to the outputs referenced respectively 01 and K1 which are themselves connected to the corresponding inputs of the circuit RPo, level II.

This circuit RPo comprises the output .I on which appears a call signal of the circuit IO and the output K constituted by the transfer conductors of the codes which identify the calling inputs in the selection circuits used in levels I and II. The distinction is thus made between:

The code Hkl of the calling input in the level I,

The code I-Ik2 of the calling input in the level II.

The code I-lk constituted by grouping these two codes identifies therefore, without any ambiguity, the calling unit Nk.

Last, each connection unit N1, N2... Ny may be selected directly by the circuit It), for instance in the search for a free junctor in a group of m junctors. For this purpose, the circuit IO selects individually a connection unit by means of one of the y selection conductors D1, D2... Dk..Dy. The signal D/t controls the setting, in the unit Nk, of the call signal Bk and, at the same time, all of the other units are reset to 0 so that the selection circuits may immediately achieve the connection between the unit Nk to the circuit IO.

l.2--Cloclt FIG. 2 represents the general diagram of the clock CU utilized for the control of the operations in the connection units and in the input-output circuit IQ of the central processor CP. The design of such a cloclt is well known and the detailed description will not be given. It comprises:

A pulse generator supplying base signals of period [/2 and of duty factor 0.5 represented on FIG. 4a;

A scale-of-two supplying alternatively timing signals a and b each one having a period oft/2 (FIG. 4b);

A divider by m+l constituted by a counter of capacity m+l numbers receiving, as advance signals, the timing signals b. An associated decoder supplies in a recurrent way signals to, t1, 12... tm of period (FIG. 40), the signal to defining the beginning of each scanning cycle. The signals t1, :2... tm are the signals which control the cyclic scanning of the inputs of the units N1, N2... Ny. The codes shown by this counter are transmitted to the circuit I0 over the group of conductors H1. The signals IO to 1m and the signals a, b are transmitted to the connection units and to the circuit IO.

2. CONNECTION UNIT 2. lDescription FIG. 3 represents the detailed diagram of the unit N1 wherein pl inputs (pil s m) or test inputs are connected to the peripheral units in order to supervise their state.

The unit Nll comprises:

The selection circuit ES of the inputs which assures, under the control of the signals :1, 12... tm applied to the AND- circuits Pat-Pam, the cyclic scanning of the inputs El, E2... Em,

The temporary memory MT which comprises m flip-flops referenced G1 to Gm, among which the p1 flip-flops of same rank as the test inputs may be used for storing the information of previous state of the corresponding peripheral units. The information which must be written in these flip-flops are received in a series form on the conductor Cd.

By way of nonlimitative example, one has shown on the figure, a memory MT equipped with JK flip-flops which receives, as clock signals, the signals :1, 12... tm at the times b. These signals control the series-parallel conversion of the data received over the conductor Cd when writing them in the flipflops.

It is realized that one may use as well, for designing this memory, RS flip-flops, the series-parallel conversion being then carried out through AND circuits controlled at the times shown on the figure.

The selection circuit SM of the flip-flops of the memory MT comprising the AND-circuits Pb] to Pbm which are successively activated by the signals ll, [2... rm assuring therefore the cyclic scanning of the states of these flip-flops and the OR- circuit P 2.

The permanent memory MP which supplies, on its output Cc, signals at the pl times corresponding to the test inputs scanning times. It is constituted by m cross-points which may or may not assure the transmission of the signals t1, t2... rm to the output Cc in order to control the selection of those of the inputs E1 to Em which are used as test inputs. Thus, on the figure, one has chosen as test inputs the inputs El, E2 and Em by making an electrical connection between the wires on which the signals til, :2 and Im appear and the conductor Cc.

The comparator OM comprising the AND-circuits Pcll, Pc2 and the exclusive OR-circuit P03. Each AND circuit comprises an activation input connected to the conductor Cc and a blocking input connected to the conductor D so that the signals supplied by the gates Pgll and P32 are applied to the circuit P03 for the logical condition CQD. This circuit delivers then a disparity signal M if the information applied on its inputs is different.

Thus, for instance, if the state of the peripheral unit j tested at time tj is different from the previous state stored in the flipflop Gj, the comparator supplies a signal M at this time tj.

The input-output circuit CA of the connection unit which comprises in particular, the JK flip-flop B and the RS flip-flop C When the call flip-flop B, which is initially in the 0 state, is set to the 1 state (for instance by a signal M), this condition means that the connection unit appears to be calling and requests to be connected to the circuit 10 of the processor.

In the same way as for the memory MT, the flip-flop B may be chosen of the types RS by adjoining to it the required control logical circuits.

Before describing the operation of the linking unit, the operation of RS and JK flip-flops will be reviewed.

In a RS flip-flop, the passage to the 1 state or to the 0 state is controlled by the application ofa signal on the l or 0 input. A voltage of same polarity as that of the controlled signals appears either on the 1 output when the flip-flop is in the 1 state or on the 0 output when it is in the 0 state with a time delay which is a function of the elements of the circuit. If the flipflop is referenced C, the logical condition characterizing the fact that it is in the l or 0 state will be written C or C. It will be noted that, if one applies simultaneously control signals on the O and 1 inputs, the final state of the flip-flop is undetermined.

In a JK flip-flop, such as the flip-fllop B, the change of state consecutive to the application of a control signal on one of the l or 0 inputs is controlled by a clock signal. The switching occurs for instance on the trailing edge of the clock pulse a so that the time delay between the triggering and the appearance of the corresponding signal on the 0 or 1 output is fixed by the duration of the clock signal. Besides, this flip-flop may be forced to the I state or to the 0 state, whatever may be the amplitude of the clock signal, by applying a control signal on the input D or Z.

2.2-Operation The operation of the connection unit Nl (FIG. ll) will be described now by recalling that this latter is calling when its flip-flop B (FIG. 3) is in the l state, which occurs either when the state of one of the peripheral units to which it is connected has changed, or when the processor CP wants to communicate with this unit.

When the peripheral unit is connected to the circuit IO (FIG. 1), there are data transfers between these two elements and, at the end, the flip-flop B is reset to the 0 state thus disconnecting the connection unit.

These various operations are grouped as follows:

2.2l-Call 2.21 I Call originating from a peripheral unit. As it has been seen hereabove, the comparator CM supplies a signal M at the time rj when the states of the input E] and of the flip-flop Gj are different and the flip-flop B is set to the 1 state. If the circuits RP]! and RPo (FIG. 1) select the unit Nll by supplying the signals ET and U11, this latter is connected to the circuit IO. The states of the inputs, those of the flip-flops of the memory MT and the output signals of the permanent memory MP are then transmitted in series form over the conductors Ca, Cb, Cc to the circuit l0, this transmission being controlled by the signals til, :2... tm. In the circuit l0, which will be described in detail under paragraph 6, one compares the received informations for identifying the input Ej so that one has thus, together with the code Hk received over the conductor K, the complete identification code of this input. All this information is transmitted to the unit CP and is processed by a subprogram chosen according to the function of the connection Operation memory OPR which contains the code characterizing the state of advancement of an operation which is being performed in the peripheral unit to which it is associated.

unit and, as the case may be, according to the state of ad- It will be noted that this memory may also be used as a vancement ofthe operation. buffer memory in which the informations sent by the circuit At the end of the data processing in the unit CP, the codes CP are 'f According to the function filled by each connection unit, and the results are sent to the circuit [0.

the flip-flops of its memory MT may receive one or several of l originating from the pr r When the 10 these assignments and some of the (mi) free inputs may be P Wants t0 Obtain data from a p ip unit l0 used as it has been seen hereabove, for transferring to the cirsend an order to said unit the circuit 10 sends, at time [0.0, a uit CP informations coming from the peripheral units. signal Z to all the connection units of the central exchange 3.2-Specialization of the conn ti n units and, during all the time to, a signal Dk to the connection unit Table l hereafter gives, by way of a nonlimitative example, Nk assigned to this peripheral unit. in the nonselected units, different types of operations which may be executed, the JK flip-flop B receives only the resetting signal Z. In the without any modification of its internal wiring, by a unit N1 the flip-flop receives moreover in t0.b, a control universal connection unit according to the invention, the signal Dk and sets thus into the 1 state. The unit N1 is then the columns giving the assignment of the inputs, of the outonly calling unit and is immediately connected to the circuit puts and of the flip-flops of the memory MT. It will be IO by means of the circuits RP] and RPO. seen nevertheless, later on, that the connection units are During times ll, :2... tm, the infonnation, such as the code specialized"as soon as they are wired.

TABLE 1 Inputs Memory MT Function Data Outputs Test gathering SUP 0RD OPR Na Line and trunk supervision X Junctor supervision X Network supervision X Network control and verification X Digit supervision X Ni Fault detection.

of peripheral unit, is transmitted to the circuit l0 and the con- Thus for the function Na of line or trunk supervision, the intinuation of the operations is also the same. puts are connected to m subscribers lines or trunks and the 2.22-Transfer of information to the selected unit. homologous flip-flops of the memory MT are used as supervi- In the two types of call, the information for the connection sion memories.

unit Nk is transmitted in series form over the conductor For the function Nb of junctor supervision, it will be as- Cd during the times 11 to tm of the cycle defined by the sumed that it comprises, not only the supervision of the state signal Dk. In the unit Nk, this signal controls the blocking 40 of the junctors but also the supervision of two half-connecof the comparator CM and the activation of the gates tions set up from each busy junctor. Pd2, P113 and the information is applied to the flip-flops Under these conditions, a number of inputs and the cor- 1 m er the complementary conductors R1 and R0 responding supervision flip-flops are assigned to these func- (inverter Pdl). tions. Besides, for each junctor, one takes two flip-flops as 2.23Disconnection. order memories and two outputs for the control of the setting- At the end of the transmission, at the time !m.b, the circuitup and of the breaking of each half-connection. AND Pd4 is activated and controls the setting to the 1 state of T function N6 of network test in a muhifieleclof is of the the flip-flop C. At the next fine time, i.e. in to.a of the followsame typ a h n i N ing cycle, the flip-flop B receives a resetting signal, For the network COl'ltlOl and verification function Nd CO"- ceming the bars of multiselectors, the order memory receives 3. UTILIZATION OF THE CONNECTION UNlTS the information related to the bars to be controlled and the inputs are used for receiving the signals characterizing the fact ofthe and of the that the operation has been carried out. One compares these the descr'pnoh of we have assumed thaw] ihpus signals to those written in the memory of orders in order to de- (pl 5 m) of the connection unit were used as test inputs tact the errors. with the P 8 pp of the memory h The fault detection function Nf consists in questioning cermsuhs therefrom P i P P' P remain tain circuits of the central exchange under the control of a available for storing therein other data such as, for inh k program stance, the codes characterizing the state of advancement h h requires; of an operation comprising several steps or orders of Orders flip-flops receiving the codes of the operations to be operations to be performed in the peripheral unit by i d t in the i it means of the corresponding output terminals of the Test inputs and the homologous supervision flip-flops which memory MT. Some of these (m-pl) available inputs may store the result which has to be obtained and which must be also be used for transferring, to the circuit CP, data colcompared to the result appearing on the test inputs. lected in the peripheral units. Last, for the digit supervision function Ne, the connection In a general way each flip-flop, or each group of flip-flops of unit operates in association with several digit receivers prothe memory MT, may receive one of the following assignvided for transforming the signals received under the form of memsl dial pulses or of voice frequencies into binary digits. Each Supervisory memory SUP which contains the previous state receiver uses then: information of one of the pl peripheral units associated to the a inlets and a supervision flip-flop which enable to carry out connection unit. This information is compared to that colits test of state (free, busy) and the supervision of the number- Iected on the homologous input. ing in course (pl=a.x),

Order memory 0RD which receives, from the processor, an d operation flip-flops which contain the code characterizing information enabling to control certain operations in the the state of advancement of the numbering (number of the peripheral unit to which it is associated. digit being reconstituted),

I; data collection inputs which enable the transfer to the processor of the digit reconstituted by the numbering receiver.

It is well understood that the rank of the operation flip-flops and of these b data collection inlets may coincide since only the information of the a inputs and supervision flip-flops are compared under the control of the signals supplied by the per manent memory MP.

TABLE II State of the inputs El-E2 State of the flipfiops and corresponding Gl-G2 and correconditions spending conditions DReceiver tree (KP-Receiver free. 11-Digit reception 11Receiver on-line. Ill-Digit complete.

01-End of numbering.

3.3-Digit supervision By way of nonlimitative examples we shall describe, in relation with the table II, the organization and the mode of operation of a connection unit specialized for performing the function Ne.

One uses, for the digit receiver R]! associated to the connection unit Nk:

The test inputs El, E2 and the supervision flip-flops G1, G2 (see FIG. 3), vizus a=2;

The operation flip-flops G3, G4, G5 (#3) which gives eight different operations codes Opll, Qp2 0 8:

The data collection inputs E3, Ed, E5, E6 (b=4) enabling the transfer, to the circuit IQ, of a digit in decimal binary code.

The operations which are carried out in a digit receiver are well known and it will be merely reminded that they comprise a succession of phases the first one of which is started by the connection of the receiver to the calling line and the following ones along as the reconstitution of the digits takes place. At the beginning of each phase, a counter is initiated defining the maximum time which may elapse up to the reception of one digit. If this time is exceded without a digit being reconstituted, the receiver is disconnected and a particular signal is sent on the calling line.

As it may be seen on table II, the fact that the inputs El, E2 and the flip-flops G1, G2 are in the 0 state means that the receiver RE is free. In the homologous flip-flop being in the same state, one has always the condition M.

When the circuit CP searches for a free receiver in order to connect it to a calling line, it calls successively the various connection units of the central exchange assigned to the function Ne by a process which will be described in paragraph 7. When both supervision flip-flops assigned to a receiver, Rll for instance, are in the 0 state, said circuit CI controls the connection of the calling line to this receiver (by performing for instance, the functions Nc and Nd).. When the connection is set up, the circuit C? calls once again the unit Nk and controls, during one cycle of signals t1-rm, the setting to the 1 state of the flip-flops G1, G2 and the sending of the first operation code Opl. At time to of the following cycle, the inputs El and E2 are in the I state so that one has the condition D71 and the code Opl controls the sending of the dial tone and the starting of the first time delay.

When one digit is reconstituted and stored in its totality in the output register of the receiver R1, the input E2 resets to the 0 state whereas the homologous flip-flop G2 is still in the 1 state so that a signal M appears and that the flip-flop Bk is set to the 1 state. When all the informations are transferred to the circuit CP, this latter processes them and sends to the connection unit Nk a signal for setting to the flip-flop G2 in the I state and the operation code Op2 etc.

When a digit is not reconstituted at the end of the time delay, the input El shifts to the 0 state, there is a discordance with the flip-flop G1 and the unit Nk calls the circuit CP. When this latter receives the information, it processes it, controls the disconnection of the receiver R1, the sending of the busy tone on the line and the setting to the 0 state of the flipflops Gll and G2 in the unit Nk.

ill

4. SELECTION CIRCUIT FIG. 5 represents a random selection circuit such as RPl... RPZ, RPo, FIG. 1.

Each selection circuit comprises a n input multistable circuit MS and a transfer circuit TG. In order to simplify the figure and the description, on has shown a circuit MS comprising n-=3 inputs to which are applied the call signals El, B2, B3. This circuit comprises n+l=4 NAND-gates referenced Pel, Pe2, Pe3, Pe t and a coder CD. It will be recalled that a NAND-gate is equivalent to an AND-circuit followed by an inverter so that, if one designates by Ya, Yb, Yc the control signals applied to the inputs of a 3-input gate and by Yo its output signal, one may write, in logical algebra: Yo=?a. YEAR or V5=Ya.Yb.Yc

It is thus seen that such a circuit delivers a signal Wonly if all the inputs receive a control signal.

Each gate Pek (in the case of the figure k=l, 2 or 3) comprises an output on which appears a signal Fk and n inputs, one of which receiving the signal E k. The n-l remaining inputs of each gate are connected respectively to the outputs of the n-l other gates (all the output signals except Fk), this feedback assuring the stability of the multistable circuit.

In order to describe the operation f this ci rcuit, we shall first assume that it receives signals B1, B2, B3 (none of the connection units to which it is connected is calling). lnthis case, each of the gates Pel, Pe2, Pe3 which receives at least one complementary signal (m for Pel, for instance) delivers a signal F1, F2, F3 and one may write, :for the gate Pel: T.F2.F3=Fll.

It is thus seen that a gate the external control signal ofwhich is absent (complementary signal Fl) supplies a signal (signal Fll) whatever may be the values of the control signals applied to the other gates. In the same way, one has:

The logical condition on the gate Fed is: F1.F2.F3=fi. This signal .li characterizes the first stable: state or the 0 state of the multistable. lf now the multistable receives the signals 81, E, E3 one may write: for the gate Pei :B1.F2.F3=fi for the gate Pe2 B2.fi.I'-'3.=-=F2 for the gate Pe3 3FTF2=F3 for the gate P24 FT.F2.F3=J.

The signal fi characterizes the second stable state or the 1 state of the multistable.

In a similar way:

The circuit is in its 2 state when only one signal B2 is applied to it, this state being characterized by the signal F2;

The circuit is in its 3 state when only a signal B3 is applied to it, this state being characterized by the signal E.

The states 1, 2 and 3 are accompanied by a signal Jll.

If two (or more) external control signals are simultaneously applied-the signals B1 and 82 for instance-one realizes that the circuit sets to either the 1 or the 2 state depending upon the very low differences of operation speed which exist always between the homologous elements of the gates Pel and Pe2.

The outputs of the gates Pel, Pe2, Pe3 are applied to the input of the coder CD constituted, for instance, by diode matrix. It supplies on its output K a code characterizing the state of the multistable, this code comprising two binary digits in the case of the example. it will be reminded that this code, referenced ll'lkl or l-lk2 in the paragraph 1.1, identifies the calling input.

It is realized that the circuit which has just been described may be directly generalized into a circuit which presents, for instance, m different stable states apart from the 0 state and which may be connected to the outputs B of In connection units.

The transfer circuit TG provided for transmitting information between one of these connection units and the circuit 10 comprises m identical groups of transfer gates such as the group TGal (FIG. 5) assigned to the unit Nl. As it has been seen during the description of FIG. 3, this information is transmitted over the group of four conductors C1 and, when this unit is selected, the signal fi (signal F1 applied to a blocking input of the AND-circuits Phl, Ph2) controls their transfer to the output Q1.

On the other hand, the signal F l controls and the transmission towards the circuit IO of the identification code (multiple AND-circuit Ph3). This transmission is carried out in series form, the series-parallel conversion being assured by the signals grouped under the reference T1. In the example of the figure, each code Hkl or Hk2 comprises two digits and one has in the circuit RPa of the level I: T'l=rl+t2 and the circuit RPo of the level II:

The circuit IO (FIG. 1) receives thus, in the time interval :1 to :4, the information consisting the identification code Hk of the calling unit Nk (information received over the input K). It receives also, during the times ll to rm: on the input On: the states of the inputs E1 to Em, on the input the states of the flip-flops G1 to Gm, on the input On: the code He constituted by the content of the permanent memory MP.

5. TOPOLOGY The connection units and the selection circuits which were described in relation with FIGS. 3 and 5 can be designed in monolithic or "large-scale" integrated circuits (LSI). FIG. 6 shows thus the topology of a group of circuits comprising n connection units Nl-Nn designed in LSI-technology and the associated selection circuit RPl which can also be designed in LSl-technology.

By way of an example, each LSI-connection unit comprises leads on its four sides which are distributed as follows:

Side l m leads are the inputs El, E2... Em (it is possible not to connect some of these leads),

Side 2 m leads are the outputs A1, A2... Am of which only those which must transmit orders to the peripheral units are connected.

Side 3 (m+l) leads are connected to the (m+l) scanning signal conductors :0 to tm.

Side 4 m leads are used as permanent memory MP (FIG. 3). The leads corresponding to the scanning times of the test inputs are the only ones which are connected to the signal conductors :1 to rm. Thus, in the unit N1, the inputs El and Em are the only test inputs and the terminals 1 and m of the permanent memory are connected to the signals :1 and 1m.

This selective connection of the terminals of the sides 1, 2 and 4 assures the specialization of the connection unit.

Besides, one has shown on this side the connection of the group of six conductors Bl-Cl-Dl particular to the unit N1.

The selection circuit RPl which receives the groups of conductors Bl-Cl-Dl to Bn-Cn-Dn and which has the outputs .I 1, Q1, K elaborates, by way of nonlimitive example, the time signals :0 to rm by means of a (m+1 position ring counter KR whose advance is controlled by the time signals b. It results therefrom that the only common conductor to the different groups of connection units is that which transmits this clock signal.

6. THE INPUT-OUTPUT CIRCUIT 6. l-Introduction The input-output circuit shown on FIG. 7 is a buffer circuit placed between the processor CP and the selection and connection circuits.

It uses a wired logic which delivers the following signals (see table III) A. Call identification signals Signal P1: call of the processor CP, Signal P2: call of peripheral unit. 8. Phase signals S, S1, S2, and S3 which act as follows:

Idle phase SO: the circuit 10 is free, no connection unit being connected to it. One call may be seized and one of the signals P1 or P2 is then set up.

Phase of data reception S1: the circuit lO receives informations from the calling connection unit which has been selected and identifies this unit. All these informations are immediately transmitted to the processor CP.

Data processing phase $2: the informations are processed in CP during a duration which is not limited. At the end of these operations, the new informations are transmitted to the circuit 10.

Data transmission S3: the informations just received by the circuit 10 are transmitted to the selected unit.

FIG. 7 represents the detailed diagram of the input-output circuit 10 in the drawing of which some simplifications have been made in order to facilitate the reading and to make the description easier. Thus:

a. Some control inputs of electronic gates receive a complex signal which is elaborated by an AND-circuit which is not shown: for instance the AND circuit which controls the setting to the 1 state of the flip-flop Y (circuit BY) receives a signal S0.t1. b. The AND and OR circuits are not referenced since they are defined without any ambiguity by the signals which are applied to them. For instance the flip-flop Y, circuit BY, is set to the I state for the logical condition SO.Y'!1 which defines perfectly the concerned AND circuit.

c. The logical condition (tl-lm) is an abbreviation of the logical condition rl+t2+... 1m.

d. The equation for the control of a flip-flop will bear the sign for instance: SO.Y'.!1 Y.

e. The element referenced RE (circuit TU) is a shift register comprising m .IK flip-flops. It comprises the inputs 0, l, the outputs 0, l and receives as clock signals the signals 53.76.42. It is used for carrying out the series-parallel conversion of the information received over the m conductors Q'c which are connected to the set" inputs of the .IK flip-flops. For the series reading, one applies to the input 0 of the register signals 53.5.0 so that the information is shifted by one rank towards the left at each scanning time except in t0 and, at the end of the cycle, all the flip-flops are in the 0 state. The output signal is gated by the fine time signal b and is written at this fine time in the corresponding flip-flop of the memory MT. The element RD (circuit TU) is a conventional register of capacity of y numbers and the element KS (circuit TC) is a four-position selector S0, S1, S2, S3 constituted by a counter and by a decoder. This selector is so designed that, when the time of the central exchange is switched on, it sets automatically in position SO.

6.2Description and operation The input-output circuit comprises:

The time control circuit TC which supplies the phase signals S0 to S3 (selector KS) and the call type signals P1, P2 defined hereabove.

The circuit RU which controls the reception of the data transmitted over the conductors Qa, Qb, 00, K and the identification of the calling input, the code Ht identifying this input is supplied by the clock CU (paragraph 1.2, FIG. 2).

The selection and transmission circuit TU which supplies the signal Z, the selection signals D1, D2... Dy of the connection units N1, N2.... Ny and the data which is transmitted over the conductor Qd.

The signals D1 to Dy are obtained by decoding the codes I-Ik applied to the inlet TD and sent by the circuit CP.

The circuit BY which supplies on the one hand a signal Y characterizing the fact that the control unit CP calls a connection unit and on the other hand a signal W characterizing the fact that the data processing in CP is completed.

Table III hereunder summarizes the different stages of operation of the circuit IO. In this table, the columns 1 and 2 represent the different phases and the column 3 the scanning times at which the elementary operations are performed. The columns 4 and 5 are assigned respectively to the operations concerning the calls of type P1 and the calls of type P2. It will be noted that the equations do not show the scanning times which are indicated in column 3 and which must be associated thereto.

These different operations will not be described in detail since all their steps are indicated in the table. However the following points will be noted:

6.2 lPhase SO. If one receives, from the unit Cl, a signal Y characterizing a call originating from the processor, one has:

S0.Y'.tll Y (at the time tll The call type identification is made in t2: SO.Y J2 Pl SCYTHE-W2 It is seen that the call from the unit C? has priority, since a call from the peripheral unit can be taken into consideration only if the condition Y is fulfilled. in the case of a P1 call, the logical condition Pl.SO.1m.a controls the writing, in the register RD, of the code Hk identifying the connection unit which must be selected. The phase changement is carried out as follows: the flip-flop Xa (circuit TC) being initially in the 1 state (signal XO=SO.!), the logical condition (Pl+P2).X a.tm.b controls the advance by one position of the selector KS which supplies a signal $1 from the beginning of the following time I0.

0003 NO CARD FOR THIS ILLUSTRATION.

6.22. Phase Sll. This phase, which lasts one cycle it) to lm, is divided into two parts:

a. Time It), for a call Pl: the condition P1511012 controls the sending by the circuit TU, of a signal Z to all the connection units of the central exchange and of a signal Dk to the connection unit which must be selected. As it has been seen, in the paragraph 2, only the unit Dk remains calling and it is connected to the processor.

b. Time ll-tm for both types of call: the logical condition Sll.(tl-A). a actiyates inthe circuit Rll the gates placed on the conductors Qa, Qb (connected respectively to the conductors Ca, Cb of the unit Nk) and K (identification code Hk of the connection unit). The information received in series form over these conductors is transmitted, as well as those received over the conductor Qc (code Hz), to the unit Cl.

At the same time, the information received on the inputs Qa, Qb is compared, in an exclusive OR-circuit which delivers a signal M when they are different. ln the case ofa call P2 a signal M" appears for the logical condition P2.M'.Qc which characterizes the fact that the states of the test input Ej and of the flip-flop Gj are different and that this input is calling.

The first signal M" controls first the transfer, over the group of conductors RD, of the e-digit code Ht (2 m 2') and second the resetting of the flip-flop V which was set in the 1 state by the signal X0 (XO=SO.!O). This resetting is carried out at the end of the fine time a at which the noncoincidence takes place and it blocks the transmission of the codes l-l! so that, if several test inputs of the unit Nk are simultaneously calling, only the identity of the first of them is noted.

At the end ofthe cycle, one has: (Pl+l2).Xa.tm.b-*S2.

6.23-Phase S2. This phase is reserved to the data processing in the unit CP and its duration is variable and may be higher than a cycle rO-!m. Therefore, the condition 8210-??? (circuit TC) controls the blocking of the advance of the selector KS.

When the processing is completed, the unit ClP sends a signal W and, at the first time t(ml one has: S2.W.t(ml).a-+W (circuit BX) then: W.tm.a a so that the selector KS is unblocked. The same logical condition W.tm.a controls the reception, in the circuit TU, of new data to be transmitted to the 1 l lll Ni(ElllQWillQlLQQlTlPllQS! The code Hk which is stored in the register RI),

The information intended for the temporary memory of the unit Nk which is stored in the shift register RE.

One has afterwards: (Pl-l- 6.24-Phase S3. The duration of this phase of data transmission is of one cycle of signals Ill-1m during which a signal Dk is sent to the unit Nk. Each signal S3.FO.a controls the shift by one position of the inforrnations in the register RE and there are transmitted at the fine times b to the unit Nk.

At the end ofthis cycle, one has: (P'll+P2 ).Xa.rm.b. -80.

7. lDENTlFlCATlON it has been seen, in the paragraphs 1.1 and 4, that the code H/t received on the input K of the circuit [0 enabled to identify the calling unit Nk.

it has also been seen at the paragraph 6.2 that, in the case of a call P2, one obtained during the phase 811 the code ll-lf identifying the calling input.

The code identifying an input is then constituted by the couple of codes Ht/ll-lk.

in the case of a call Pll, the part Hk of this code is used for selecting the connection unit and the final selection of the input is carried out, in the unit CP, by means of the code Hr.

On the other hand, a part of this code Hk, vizus the code Hk', may be used for identifying, when receiving of data in the unit CP (phase Sll), the type of operation for which the connection unit is specialized.

in a reverse way, when the processor wants to search for a free peripheral unit, one obtains the codes of these units by adding to the code We characterizing the function, a cyclic series of codes Hk", each couple of codes Hk'll-lk" constituting the code l-lk ofa connection unit specialized in this function.

During the phase 511, one receives also the code Hc constituted by the content of the permanent memory MP (FIG. 3), and which contains ls at the time positions corresponding to test inputs. it is realized that this code is different according to the function for which the connection unit is specialized and that, even for a given function, one may easily obtain dif ferent codes according to the connection units. Thus for instance, for a unit specialized in the :function Na, the code is l l l l 1... since each input is used for a line or trunk test. Nevertheless if one does not connect one input out of In, one may obtain m different codes such as Ol l l 1, l0] 1 1 etc.

These codes Hc may be used, as an alternative to the preceding solution, for identifying the type of function in which the connection unit is specialized, or for carrying out a preselection.

Thus, the function Na may be subdivided in: Nail incoming trunks-code He Di 1 l l l l... Na2 Outgoing trunl scode He: 10] ll l l,.. Na3 Normal lines-code He: 1101 l l... Na4 Priority lines:code ll-lc: l l 101 l l... NaS Conference lineszcode He: 1 l l 10! l l... N116 Lines having no access to the external network-code Hc:lllll01...etc.

When one of these peripheral uniits appears to be calling, the decoding of its code l-lc enables to know immediately its category without having to refer to a memory of the processor While the principles of the above invention have been described in connection with specific embodiments and particular modifications thereof it is to be clearly understood that this description is made by way of example and not as a limitation of the scope of the invention.

We claim:

1. A connection unit for providing connections between peripheral equipment associated with a telephone exchange system and a central processor associated with the central exchange comprising a plurality of peripheral units, m inputs connected to x peripheral units (where xsm) in order to receive test input signals, a temporary memory with m flipflops in which may be written the previous state of the peripheral units as indicated by test input signals as well as operation codes, and m outputs associated with the m flipflops, a portion of said outputs being connected to the peripheral units in order to send orders represented by the operation codes written in the corresponding flip-flops.

2. A connection unit as claimed in claim ll, forming one of a group of n connection units coupled to a selection circuit which controls the transfer, to the processor, of information collected by only one calling peripheral equipment, even if several units of equipment are simultaneously calling, and

means disposing of two selection stages in series when the total number of connection units is greater than n.

3. A connection unit as claimed in claim 1, in which the connection unit includes a permanent memory and an inputoutput circuit including a call flip-flop, the permanent memory provides signals of use in controlling the cyclic scanning of the test inputs and the comparison of the infonnation obtained with the homologous previous-state infonnation, and in case of disparity, the connection unit calls a central processor by setting the call flip-flop to the 1 state.

4. A connection unit as claimed in claim 2, in which results of processing data in the processor are transmitted to the calling unit.

5. A connection unit as claimed in claim 2, in which a central processor is coupled to collect from and to transmit information to a connection unit, and it sends to the connection unit a signal which makes it calling and which resets to zero the call flip-flops of all the other units of the central exchange.

6. A connection unit as claimed in claim 1, including a main clock delivering in a cyclic way signals to :1, 12,... rm of equal duration, m inputs E1, E2... Em of the connection unit selected cyclically by the signals :1, t2... rm, a temporary memory comprising m flip-flops G1, G2... Gm the outputs of which are selected by the signals t1, t2... tm, a permanent memory delivering a signal Cc at each of the pl scanning times (where pl s m) which correspond to pl test inputs which are connected to peripheral units in order to test their state, a comparator which delivers, at time I], a disparity signal M when the state of the test input Ej is different from that of the flip-flop Gj, and an input-output circuit comprising a call flipflop B which is put to the I state either by a signal M or by the control processor of the telephone exchange when this latter wants to select the considered connection unit.

7. A connection unit as claimed in claim 6, in which the permanent memory supplies a series of signals Cd during one cycle of the scanning signals :1, 12... tm, said signals Cd serving as a code characterizing the type of function fulfilled by the connection unit, and the functions for which pl=m may be differentiated the ones from the others in leaving free one input of different index according to the function.

8. A connection unit as claimed in claim 1, forming one ofa group of m connection units in which a connection to an input-output circuit of a central processor is carried out through selection circuits grouping n connection units, said selection circuits being connected so that there is a multilevel selection, each of said selection circuits comprising a multistable circuit with n+1 stable-states and a transfer circuit assuring a bidirectional transfer of data between a selected connection unit NK and the input-output circuit, the first selection level comprising z selection circuits, means connecting the multistable circuit of each selection circuit to the l outputs of the call flip-flops of n connection units, said circuit delivering when the call flip-flop Bk of the unit Nk is in the l state an activation signal of the transfer gates associated with said unit and a call signal of the next selection level and if several connection units are simultaneously calling said multistable circuit choosing one of them without ambiguity and at random.

9. A connection unit as claimed in claim 8, in which the processor is able to select directly the unit Nk, the processor transmits simultaneously a signal Z and a signal Dk at a time to, the signal Z is transmitted to all the connection units of the central exchange which resets all the call flip-flops, the signal Dk is transmitted to set the flip-flop Bk to the 1 state so that only the unit Nk is calling and it may be immediately connected to the input-output circuit, the signal Dk being delivered by the decoding of the identification code of the unit Nk.

10. A connection unit as claimed in claim 10, in which the unit Nk is selected by the'call either of a peripheral unit or by the control unit, the states of the inputs El, E2... Em and of the fiip-flops G1, G2... Gm are transferred, through the various selection stages, to the input-output circuit as well as the identification codes of the connection units and of the used selection circuits that, and when the call originates from a peripheral unit, the comparison of these signals in the said input-output circuit gives the identification code of the first input whose state has changed and this information is processed under the control of the processor.

11. A connection unit as claimed in claim 8, in which after data processing is completed in the processor, a signal Dk is transmitted to the unit Nk to block the operation of said unit and the information supplied by the processor is transferred to said connection unit under the control of the signals ll, 12... tm. 

1. A connection unit for providing connections between peripheral equipment associated with a telephone exchange system and a central processor associated with the central exchange comprising a plurality of peripheral units, m inputs connected to x peripheral units (where x m) in order to receive test input signals, a temporary memory with m flip-flops in which may be written the previous state of the peripheral units as indicated by test input signals as well as operation codes, and m outputs associated with the m flip-flops, a portion of said outputs being connectEd to the peripheral units in order to send orders represented by the operation codes written in the corresponding flip-flops.
 2. A connection unit as claimed in claim 1, forming one of a group of n connection units coupled to a selection circuit which controls the transfer, to the processor, of information collected by only one calling peripheral equipment, even if several units of equipment are simultaneously calling, and means disposing of two selection stages in series when the total number of connection units is greater than n.
 3. A connection unit as claimed in claim 1, in which the connection unit includes a permanent memory and an input-output circuit including a call flip-flop, the permanent memory provides signals of use in controlling the cyclic scanning of the test inputs and the comparison of the information obtained with the homologous previous-state information, and in case of disparity, the connection unit calls a central processor by setting the call flip-flop to the 1 state.
 4. A connection unit as claimed in claim 2, in which results of processing data in the processor are transmitted to the calling unit.
 5. A connection unit as claimed in claim 2, in which a central processor is coupled to collect from and to transmit information to a connection unit, and it sends to the connection unit a signal which makes it calling and which resets to zero the call flip-flops of all the other units of the central exchange.
 6. A connection unit as claimed in claim 1, including a main clock delivering in a cyclic way signals to, t1, t2,... tm of equal duration, m inputs E1, E2... Em of the connection unit selected cyclically by the signals t1, t2... tm, a temporary memory comprising m flip-flops G1, G2... Gm the outputs of which are selected by the signals t1, t2... tm, a permanent memory delivering a signal Cc at each of the p1 scanning times (where p1 m) which correspond to p1 test inputs which are connected to peripheral units in order to test their state, a comparator which delivers, at time tj, a disparity signal M when the state of the test input Ej is different from that of the flip-flop Gj, and an input-output circuit comprising a call flip-flop B which is put to the 1 state either by a signal M or by the control processor of the telephone exchange when this latter wants to select the considered connection unit.
 7. A connection unit as claimed in claim 6, in which the permanent memory supplies a series of signals Cd during one cycle of the scanning signals t1, t2... tm, said signals Cd serving as a code characterizing the type of function fulfilled by the connection unit, and the functions for which p1 m may be differentiated the ones from the others in leaving free one input of different index according to the function.
 8. A connection unit as claimed in claim 1, forming one of a group of m connection units in which a connection to an input-output circuit of a central processor is carried out through selection circuits grouping n connection units, said selection circuits being connected so that there is a multilevel selection, each of said selection circuits comprising a multistable circuit with n+1 stable-states and a transfer circuit assuring a bidirectional transfer of data between a selected connection unit NK and the input-output circuit, the first selection level comprising z selection circuits, means connecting the multistable circuit of each selection circuit to the 1 outputs of the call flip-flops of n connection units, said circuit delivering when the call flip-flop Bk of the unit Nk is in the 1 state an activation signal of the transfer gates associated with said unit and a call signal of the next selection level and if several connection units are siMultaneously calling said multistable circuit choosing one of them without ambiguity and at random.
 9. A connection unit as claimed in claim 8, in which the processor is able to select directly the unit Nk, the processor transmits simultaneously a signal Z and a signal Dk at a time to, the signal Z is transmitted to all the connection units of the central exchange which resets all the call flip-flops, the signal Dk is transmitted to set the flip-flop Bk to the 1 state so that only the unit Nk is calling and it may be immediately connected to the input-output circuit, the signal Dk being delivered by the decoding of the identification code of the unit Nk.
 10. A connection unit as claimed in claim 10, in which the unit Nk is selected by the call either of a peripheral unit or by the control unit, the states of the inputs E1, E2... Em and of the flip-flops G1, G2... Gm are transferred, through the various selection stages, to the input-output circuit as well as the identification codes of the connection units and of the used selection circuits that, and when the call originates from a peripheral unit, the comparison of these signals in the said input-output circuit gives the identification code of the first input whose state has changed and this information is processed under the control of the processor.
 11. A connection unit as claimed in claim 8, in which after data processing is completed in the processor, a signal Dk is transmitted to the unit Nk to block the operation of said unit and the information supplied by the processor is transferred to said connection unit under the control of the signals t1, t2... tm. 